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Lung function tests check to see how well your lungs work, and to see if your lungs are the cause of your symptoms. These tests can find lung problems, measure how serious they are, and check to see how well treatment for a lung disease is working.
Much like having your blood pressure tested before taking blood pressure medicine, a breathing test (lung function test) is the appropriate first step that could help to identify lung disease.
The tests look at:
Types of lung function tests include:
Lung function results are measured directly in some tests and are calculated in others.
No single test can check for all of the lung function values, so more than one type of test may be done. Some tests may be repeated after you inhale medicine that enlarges your airways (bronchodilator).
Sometimes other tests are done at the same time as lung function tests. For example, you may have a blood test to check the oxygen and carbon dioxide levels in your blood (arterial blood gas test or ABG). This isn’t a lung test, but it can help to tell how well your lungs are working. Or you may have a small sensor attached to your finger to check the oxygen level in your blood (oximetry).
There are several different types of lung function tests. You may also hear these tests called pulmonary function tests, or PFTs. A complete or full PFT usually involves most of the types of tests listed above, but a full PFT is not always necessary. For example, to diagnose asthma or COPD, only the spirometry test is necessary.
Spirometry is the most common lung function test. It measures how much and how quickly you can move air into and out of your lungs. You breathe into a mouthpiece attached to a recording device.
This test can measure many different things about the way you breathe and whether you respond to a reliever medicine.
Gas diffusion tests measure the amount of oxygen and other gases that move through the lungs' air sacs (alveoli) per minute. These tests let you know how well gases are being absorbed into your blood from your lungs. Gas diffusion tests include:
Lung volume testing (also called Body plethysmography) may be used to measure:
Inhalation challenge tests are done to measure how your airways respond to substances that may be causing asthma or wheezing. These tests may also be called methacholine or bronchoprovocation tests.
During the test, you inhale increasing amounts of a substance through a nebulizer. This is a device that uses a face mask or a mouthpiece to deliver the substance in a fine mist (aerosol). Spirometry readings are taken to look at lung function before, during, and after you inhale the substance.
Exercise stress tests look at how exercise affects your lungs. Spirometry readings are done before and immediately after exercise.
Lung function tests are done to:
Lung function tests are usually done in special rooms that have all of the right equipment.
For most of the tests, you'll wear a nose clip to keep air from leaking through your nose. Then you'll breathe into a mouthpiece connected to a recording device.
The exact steps depend on which test you have. For example, you may be asked to inhale as deeply as you can and then to exhale as fast and as hard as you can. You also may be asked to breathe in and out as deeply and as fast as you can for 15 seconds.
Some tests may be repeated after you have inhaled a spray (puff) containing medicine that expands the airways in your lungs. You may be asked to breathe a special mixture of gases, such as 100% oxygen, a mixture of helium and air, or a mixture of carbon monoxide and air.
If you have gas diffusion or lung volume tests, you will be asked to sit inside a small glass booth with big windows all around that allow you to see out.
The accuracy of the tests depends on how well you can follow all of the instructions. The healthcare professional will coach you and may ask you to breathe deeply during some of the tests to get the best results.
The testing may take from 15 to 60 minutes, depending on how many tests you have.
Lung function tests are usually painless. Some of the tests may be tiring for people who have a lung disease.
You may cough or feel light-headed after breathing in or out rapidly, but you will be given a chance to rest between tests. It may not be comfortable to wear the nose clip or to breathe through the mouthpiece.
If you have gas diffusion or lung volume tests, you may feel uncomfortable in the airtight glass booth. But the healthcare professional will be nearby to open the door if you feel too uncomfortable.
If you are given breathing medicine, it may cause you to shake or may increase your heart rate. If you feel any chest pain or discomfort, tell the healthcare professional right away.
If you have an arterial blood gas test, you may feel some pain from the needle used to collect the blood.
For a healthy person, there's little or no risk in taking these tests. If you have a serious heart or lung condition, discuss your risks with your doctor.
A specially trained doctor will interpret the information that is collected during your tests. The results are usually ready within 3 days.
Results are in the normal range for a person with healthy lungs.
Test results are outside of the normal range for a person with healthy lungs. This may be a sign of some kind of lung disease.
Obstructive lung conditions cause the airways to get narrower.
Examples include emphysema, bronchitis, asthma, and infection that produces inflammation.
Lung function test
What the test measures
Result as predicted for age, height, sex, weight, or race
Forced vital capacity (FVC)
How much air you can exhale with force after you inhale as deeply as you can.
Normal or lower than predicted value
Forced expiratory volume (FEV1)
How much air you can exhale with force in one breath.
FEV1 divided by FVC
See the first two tests above.
Forced expiratory flow 25% to 75%
How much air you can breathe out halfway through an exhale.
Peak expiratory flow (PEF)
How much air you can quickly exhale when you try your hardest.
Maximum voluntary ventilation (MVV)
The greatest amount of air you can breathe in and out during 1 minute.
Slow vital capacity (SVC)
How much air you can slowly exhale after you inhale as deeply as you can.
Normal or lower
Total lung capacity (TLC)
The amount of air in your lungs after you inhale as deeply as you can.
Normal or higher
Functional residual capacity (FRC)
The amount of air in your lungs at the end of a normal exhaled breath.
Residual volume (RV)
The amount of air in your lungs after you have exhaled completely.
Expiratory reserve volume (ERV)
The difference between the amount of air in your lungs after a normal exhale (FRC) and the amount after you exhale with force (RV).
RV divided by TLC ratio
See the test above.
Restrictive lung conditions cause a loss of lung tissue, a decrease in the lungs' ability to expand, or a decrease in how well the lungs can transfer oxygen or carbon dioxide in or out of the blood.
Examples include scleroderma, pulmonary fibrosis, and sarcoidosis. Other restrictive conditions include some chest injuries, being very overweight (obesity), pregnancy, and loss of lung tissue due to surgery.
Lower than predicted value
Normal, lower, or higher
Adaptation Date: 4/5/2023
Adapted By: Alberta Health Services
Adaptation Reviewed By: Alberta Health Services
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